DAP (Diammonium Phosphate)

DAP — Diammonium Phosphate, chemical formula (NH₄)₂HPO₄ — is one of the most widely used synthetic fertilisers in Indian agriculture. It contains 18% nitrogen (as ammonium) and 46% phosphorus (as P₂O₅), making it the highest-analysis P fertiliser commercially available. Its high P concentration per kg means lower transport cost per kg of nutrient delivered, and its dual N-P composition simplifies field application by combining two nutrients in a single granule.

DAP is produced industrially by reacting anhydrous ammonia with phosphoric acid: 2 NH₃ + H₃PO₄ → (NH₄)₂HPO₄. The raw materials are rock phosphate (mined in Morocco, Russia, Jordan, and China) and natural gas (used to produce ammonia via the Haber–Bosch process). India imports more than 50% of its annual DAP requirement of approximately 12 million tonnes and 90%+ of its rock phosphate — making DAP price extremely sensitive to global energy and shipping costs. The 2022 supply disruption following Russia's invasion of Ukraine sent international DAP prices from $500 to $1,000+ per tonne; subsidies were significantly increased to keep retail farm-gate prices steady at ₹1,350 per 50 kg bag.

Agronomically, DAP is the primary planting-time (basal) fertiliser for cereals (rice, wheat), pulses, oilseeds, and most horticultural crops. It is broadcast or band-placed at sowing because phosphorus is immobile in soil and must be positioned within reach of developing roots. The ammonium nitrogen component releases over 2–4 weeks as nitrification occurs, supporting early-stage growth. DAP is alkaline-reacting in the granule but slightly acidifying in the soil after full mineralisation — repeated long-term use requires lime correction on already-acidic soils. The relevance to biogas digestate fertiliser is competitive: every tonne of P₂O₅ delivered through digestate or Phosphate-Rich Organic Manure (PROM) — typically priced at ₹6,000–10,000 per tonne — competes with DAP at ₹1,350 per 50 kg bag pre-subsidy or ₹2,500–3,000 per 50 kg bag post-subsidy. Without the FCO-registered PROM premium, digestate phosphorus struggles to compete with subsidised DAP on per-kg-P basis. The strategic case for digestate-P is that PROM and FOM also deliver organic carbon, micronutrients, and soil-biology benefits that DAP alone cannot — supporting a value-based rather than price-based positioning.